For fine aggregate samples, the requirement is that the sample in the bag remains on the suspension for at least 15 minutes and the immersed mass is recorded.

• A. True
• B. Not specified
• C. Only for coarse aggregates
• D. False

Answer: (A)

When evaluating fine aggregate, getting accurate density and absorption measurements depends on how the material behaves in water. Fine aggregates are highly porous, so air trapped in the pores can distort buoyancy and yield misleading weights. To prevent that, the sample is placed in a bag and suspended in water long enough for the pores to become fully saturated and for any entrapped air to escape. A minimum soak of 15 minutes gives a stable, saturated condition and ensures the measurement reflects true immersion.

After this period, the immersed mass is recorded—the weight of the bag and aggregate while completely submerged. This immersed mass, together with the dry mass, is used to calculate how much water the aggregate displaces and its density when submerged, which in turn provides the specific gravity and absorption values needed for mix design and quality control. If the immersion time is too short, incomplete saturation or remaining air pockets would bias the submerged weight and lead to incorrect results.

This requirement is specific to fine aggregates; coarse aggregates use a different procedure, so identifying that this rule applies to fine aggregates is correct.